something to look for

[Neil Harvey]

I was cruising the internet tonight (don't get a lot of time to do) and came across a guy by the name of "Kav" rebuilding his Porsche engine. It was part one, where he assembles his case and lower assemblies.

In the video he goes over the work done to the engine case by his chosen machine shop. In his narration he states the case halves were decked and the main housing machine back to standard.

Unless it was some odd camera angle, the main "caps" show shadowing at the parting line on all. Only one side was shown, but I would expect this to be the same the other side as well. He did not show measuring the housing bores for size nor the ID of the bearing shells.

Here is what is important to know. The housings want to be round with an out of round acceptable amount of +/- 0.0004", if you aim for the middle of the spec. Ideally, you should machine to 1/2 of that and use the spec size either the lower end or the upper end as the bore overall size. This keeps the out of round where it wants to be and the overall size within the tolerance.

Why, to clamp the shell correctly and make sure once the shells are fitted and the other side is clamped together with its mate, the bearing ID is round. The biggest influence on making sure the ID of the bearing is round is at the parting line.

In this case, there was quite a lot of shadowing at the parting line, which give me cause to think the final ID of his main bearing may not be as they should. The clearance to the journal may be larger than expected and could have some affect on oil pressure.

If you deck the case halves to bore the main housing back to the standard size, why is there shadowing showing??

The only way to know is to check. Do not assume the case is machined correctly. The case should be assembled without the shells and the housing bore measured. Then the shells should be fitted and the bearing ID's measured, along with the crank journals and the clearances calculated.

So my advice here is, never trust anyone and never assume the work done is done correctly. You are the assembler its on you to check and make sure. Don't blame the machine shop after you assemble the engine and find a problem. They may have given you back wrongly machine parts but it's your responsibility as the assembler to check.

I have a saying, "nothing will humble a man more than an engine or an angry wife!"